Induction lamp



L. H. SABINE Aug. 20, 1957 INDUCTION LAMP Filed Feb. 16, 1956 INVENTOR:L.4UR/ H $45M ATTORNEY United States Patent Q INDUCTION LAMP Laurie H.Sabine, Beverly, Mass., assignor to Sylvania Electric Products Inc.,Salem,Mass., a corporation of Massachusetts Application February 16,1956, Serial No. 565,842

7 Claims. or. 313-161) This invention relates to induction lamps, thatis to lamps in which a refractory body, called a target, is inductivelyheated to incandescence.

The heating is generally achieved by placing a coil around therefractory body and passing a high frequency current through the coil. Afield concentrator is used between the target and the coil, theconcentrator generally including an annular disc around the target butspaced from it. The disc has a radial slot to prevent circulation ofcurrents in a complete ring around the target. The latter is generally acircular cylinder in shape, and is centrally located inside the centralcircular opening of the concentrator disc.

While such an arrangement gives a far more uniform light distributionthan can be obtained from a coiled incandescent filament, the lightoutput will nonetheless be smaller from the target area in the vicinityof the slot than it will be in other regions of the target. Thebrightness is about 20% less near the slot than it is on thediametrically opposite portion of the target. Such a variation ispermissible for many purposes, but is undesirable in the printing ofmotion picture film, for example.

I have discovered that a much greater uniformity can be obtained byplacing the target eccentrically in the concentrator opening, so thatthe target will be nearer to the circumference of the central openingnear the radial slot than it is to the circumference at the oppositeclosed portion of the circumference. Such an arrangement is useful wherethe spacing between the target and circumference of the central openingdoes not become so small that crystal growth across it from the targetwill greatly shorten the life of the lamp. j

I have further discovered that uniformity of brightness over the forwardarea of the'target can be achieved by having the radius of curvature ofthe opening increase around the opening as the distance from the slotincreases. The opening can be made oval in shape, so that it projectsconsiderably outward from the base circle at a region diametricallyopposite to the slot.

In addition, the slot should be made as narrow as possible, and thetarget set so that it extends somewhat beyond the plane of theconcentrator disc in the direction of useful light emission, for bestresults.

Other objects, features and advantages of the invention will be apparentfrom the following specification, together with the accompanying drawingin which:

Fig. l is a plan View of concentrator and target, with a glass envelopearound the same; i

Fig. 2 is a side view thereof, in section;

Fig. 3 is an enlarged view of the central opening of the disc of Fig. l;and

Fig. 4 is a view of a circular central opening with an eccentric target.

In Fig. l, the concentrator disc 1 is inside but spaced from the tubularglass envelope 2, shown in section. The disc 1 has the narrow radialslot 3, terminating in an oval central opening 4, having the projectingbump or extension 5 diametrically opposite slot 3. The target 6 is acylinder of refractory material such as tantalum carbide, set inside,but spaced from the opening 4 in the concentrator disc 1, and set atabout the center of the base circle from which the bump 5 extends.

Fig. 2 shows the glass envelope 2 with its flat top portion 7, throughwhich light from the front surface 8 of target 6 is emitted. The target6 extends forward of the plane of the disc 1. Placing the target toextend forwardly in-that manner further improves the uni formity oflight output.

The hollow tubes99 are attached to the cylindrical portion 10 extendingdownward from the concentrator disc 1 and in electrical contacttherewith around the outer circumference of said disc. The stem 11, ofsmaller diameter but of the same material as target 6 is attached to thesame and extends into the zirconium tube 12 which supports it as shownin copending application Serial No. 520,718, filed in the United StatesPatent Office on July 8, 1955 by Sandford C. Peek. The latterapplication also shows complete details of the construction of aninduction lamp, the present application accordingly show ing only suchparts as are necessary to illustrate the improvement claimed herein.

The slot 3 should be made as narrow as possible with out shortcircuiting or arcing, a width of about ,4, inch being satisfactory withone embodiment of my device. In the same embodiment, the target has adiameter of inch and depth of inch. The opening 4 was based on a circleof 0.390 inch diameter, with the projection 5 extending to a distance of0.400 inch from the circumference directly opposite at the slot. Thetarget is set in the opening 4 with a slight eccentricity, so thatdistance from target edge to circumference of concentrator opening is0.028 inch near the slot 3 and about 0.035 inch along a diameterperpendicular to the center line of the slot.

The projecting portion is rounded off to a circumference of 0.200 inchdiameter, the other edges of the pro jection being tangent to the maincircle and the 0.200 inch circle.

Fig. 3 shows a more enlarged portion of the concentrator disk 1, toindicate its shape in more detail.

In Fig. 4, the opening 4 is circular, and the target 6 is a circularcylinder, set eccentrically in said opening.

Although tantalum carbide, TaC has been given as an example of a targetmaterial, other sufficiently refractory materials, such as niobiumcarbide or hafnium carbide, can be used.

What I claim is:

1. An induction lamp comprising a refractory target, a magnetic fieldconcentrator around said target, said concentrator having a centralopening at a substantially greater distance from the outside rim of thetarget at some points on said rim than at others.

2. An induction lamp comprising a cylindrical refractory target, amagnetic-field concentrator around said target, said concentratorincluding a disc having a central generally oval opening therein, asdistinguished from a circular opening, the target being inside saidopening but spaced therefrom. Y

3? The combination of claim 2, in which the target has a substantialportion in front of the plane of said concentrator disc in the directionof useful high emission.

4. The combinationof claim 2, in which the concentrator has radial slotof very narrow dimensions.

5. The combination of claim 2, in which the concentrator has a verynarrow radial slot, and the opening has a major axis along theprojection of said radial slot.

6. An induction lamp comprising a refractory target, a magnetic fieldconcentrator around said target, said t 3 concentrator having a centralopening whose distance References Cited in the file of this patent fromthe rim of the target increases as the distance from UNITED STATESPATENTS the slot increases. 7

7. An induction lamp comprising a refractory target, 2*171359 Garner1939 a magnetic field concentrator around said target, said 5concentrator having a central opening said target being set in saidopening eccentrically but spaced fr om it; I

1. AN INDUCTION LAMP COMPRISING A REFRACTORY TARGET, A MAGNETIC FIELDCONCENTRATOR AROUND SAID TARGET, SAID CONCENTRATOR HAVING A CENTRALOPENING AT A SUBSTANTIALLY GREATER DISTANCE FROM THE OUTSIDE RIM OF THETARGET AT SOME POINTS ON SAID RIM THAN AT OTHERS.